Hi,
Unfortunately, FMOD does not natively support reflections. However, the Resonance Audio (Fundamental Concepts - Early Reflections and Reverb) plugin does have early reflections which we do support (FMOD Studio | Advanced Topics - Resonance Audio) and is included with FMOD Studio.
I would suggest giving the resonance audio documentation a read to see if it supports the functionality you are looking for.
What engine are you looking at developing on?
Hope this helps!